Synchronous motor



Dec. 18, 1934. o. JANZEN SYNCHRONOUS MOTOR Filed Sept. 25, 1933 0 JynyrzPatented 18, 1934 "1,981,621;

UNITED STATES PATENT \OFFICE 1.984.929 I SYNCHBONOUS MOTOR Otto Janun,Berlin, Germany Application September 25, 1933, Serial No. 690,885

In Germany September 29, 1932 4 Claims. (Cl. 172-275) My nvention reates to sync onous motors. two flanged members 6 and v, and thesandwiched and it is an object of my invention to provide a member 8,and in which the rotor 9 extends all motor of this type which isparticularly suitable over the poles or teeth of the stator, while the rfor the operation of talkingmachines. coils 15 and 16 are housed inrecesesses of the Synchronous motors are old in which a single flangedmembers; is a preferred embodiment. 5

exciting coil of annular form is arranged inter- Other designs ofstators may be provided without mediate the stator and the rotor so asto excite departing from my invention.

both parts at the same time. With the object In the old or single-coiltype of motor referred Of y invention n ISubdiVide t t ng to, the forcelines extend as shown in Fig. 3,

1o coil into two spaced-apart coils which are conthat is, they enclosethe single coil C and penenected in opposition, and insert a member oftrate the stator and the rotor uniformly and submagnetic materialbetween the inner faces of the stantially homogeneously in planes whichare two coils. radial to the axis of the rotor R.

The old single-coil motors are quite satisfactory Motors of this generaltype are particularly 10 for the playing of sound records but, if usedfor suitable for the operation of talking machines the making of soundrecords, they possess cerbecause it is easy to design them asmulti-polar tain drawbacks which are eliminated by the d011- andconsequently slow-speed motors. The poles ble-coil motor according to myinvention, as will or teeth are arranged in two concentric rows on beexplained below. the stator and the rotor and the force lines cross Inthe accompanying drawing, a motor emthe air gap G twice, and in oppositedirections. 20 bodying my invention is illustrated by way of For theplaying of sound records, such motors,

example. as mentioned, are quite satisfactory as the power In thedrawing demand is small, the motor does not heat up ex- Fig. 1 is anaxial section of the motor, cessively and its leakage field is so weak,particu- Fig. 2 is a diagram showing the connection of larly if thestator is of cast iron, that it will not 25 its coils in opposition, andinterfere even with the most sensitive electric Fig. 3 is a diagram ofthe force lines in the old pick-up on the talking machine. single-coilmotor. For making sound records, however, the pow- Referring now to thedrawing, and first to Fig. er demand is higher than for playing and theex- 1, the rotor shaft 1 is mounted in suitable bearcitation of the coilC must be increased if the size 30 ings 2 and 3 of the end plates 4 and5. The two of the motor is not to become very large. The end plates 4and 5, two flanged members 6 and increased excitation of the coil 0increases the '7, and an annular member 8 which is sandwiched magneticsaturation of the path of the force lines, between the inner faces ofthe flanged members and also the leakage. This is particularly trou- 6and 7, make up the stator. The rotor 9 is blesome at the upper side ofthe motor where the 35 mounted on the shaft 1 with its boss 10. It isleakage lines penetrate into the iron record bearpreferably madein onepiece and is equipped with er- The t e d t S to y pp the usual rotorteeth 11 at the perimeter, correciable extent when the record is madebut when sponding stator teeth 12, 13 and 14 being formed the record isplayed, heavy humming at the syson the flanged members and the annularmember. tem frequently will occur. It has been attempted 40 Two annularexciting coils 15 and 16 are to place Screening p es below the recordbearmounted in recesses of the flanged members 6 er but the trouble isnot eliminated altogether, and 7 at opposite sides of the annular memberand there is the extra cost of the screening plates. 8. The two coils l5and 16 are connected in Another drawback of the old single-coil motorsopposition, as shown in Fig. 2 where 17 is a supis that they behave liketransformers electro- 45 ply conductor, and 18 a return conductor. Themagnetically. e eXciting coil corresponds current flows anti-clockwisein coil 15, and clockthe P y w d of the transformer. and the wise incoil 16. annular closed masses of iron in the stator and The number ofthe teeth 11 on the rotor 9 is the rotor correspond to short-circuitedsecondequal to that of the teeth 12, 13 and 14 on the ary windings.Although the eddy, or rather sec- 5 stator members 6, 7 and 8. Thesandwiched ondary, currents in the iron parts are much remember 8 is ofmagnetic material which preferduced because the stator and the rotor areof ably is the same as the material of the stator, norcast iron whichreduces the specific resistance mally cast iron. of the iron parts, theeddy or secondary currents The stator which has been illustrated, withthe still were so strong as to cause an appreciable 55 heating of themotor and to limit its power output.

Another drawback is that the eddy or secondary currents in the statorand the rotor produces a strong magnetic field which interferes with thepick-up like the proper field of the coil C. Moreover, the field of theeddy or secondary currents is distorted in phase with respect to theproper field of the coil, and so the resulting field from both neverbecomes zero and it is not easy for the pole teeth of the motor tooverstep the border between the range of one stator tooth and the nextone.

By subdividing the exciting coil of the old motor in the mannerdescribed, I obtain a motor which is superior to the single-coil motorin that its excitation and output are increased without undulyincreasing the leakage and the heating and the motor develops more powerwithout being made larger.

According to my invention, as described, I provide two individual coilsinstead of a single coil. The two coils and 16 are connected inopposition (Fig. 2) and are arranged one above the other, with theannular member 8, of magnetic material, preferably cast iron, sandwichedbetween them and equipped with pole teeth 14.

The polarities of the stator and the rotor are indicated by the lettersN and S in Fig. 1. Each coil 15 and 16 is surrounded by a magnetic fieldwhose force lines extend in planes radial to the axis of the rotor andenclose the corresponding coil. As the coils are connected in oppositionthe direction of the fields in the sand wiched member 8 is the same, asshown by the arrows in Fig. 1. The rotor 9 which, as mentioned, ispreferably made in one piece, extends all over the three rows of polesor teeth 12, 13 and 14 in the stator, and the force lines cross the gapG at three points, and not at two, as in the old motor, Fig. 3.

Comparing the diagram in Fig. 3 with the section in Fig. 1, it will befound that for equal field intensity and power the fields above andbelow the coils 15 and 16 are only one-half of the field in the oldmotor, Fig. 3, while in the space between the two coils 15 and 16 thetwo equi-directional half fields combine into a resultant field which isequal to the field in the old motor. The watt consumption is only aboutone-half of that in the old motor.

This distribution of the fields has for its consequence that thesaturation above and below the coils 15 and 16 is only one-half of thatin the old motor and so there will be no troublesome leakage even if theexcitation is increased. The field has no tendency to penetrate into therecord bearer and the pick-up, as it does in the old motor.

As the coils 15 and 16 are connected in opposition, the currents inducedby their proper fields are oppositely directed and therefore the eddy orsecondary currents in the iron of the stator and the rotor do not becomeeffective. The suppression of the said currents and their fieldseliminates not only the heating they produce, and the limit set to thepower of the motor by such heating, but also the phase distortion withthe proper fields of the coils 15, 16, so that the proper fields actfreely on the rotor teeth 11.

I claim:

1. In a synchronous electric motor in combination a stator, a rotor. anexciting coil which is subdivided into two single coils connected inopposition, arranged axially. one above the other and coaxially to themotor axis, an alternating current source which excites the two singlecoils simultaneously with the same frequency, a magnetizable annularmember between the two single coils in which member the force lines ofthe two single coils are added while the secondary currents in statorand rotor are suppressed.

2. In a synchronous electric motor according to claim 1, wherein thestator, the rotor and the magnetizable annular member are made of castiron.

3. In a synchronous electric motor according to claim 1, the stator ismade of cast iron and provided with teeth, the rotor being made of castiron and provided with teeth and the magnetizable annular member beingmade of cast iron and provided with the same number of teeth as thestator and the rotor.

4. In a synchronous electric motor according to claim 1, wherein thestator comprises an upper pole ring surrounding the upper part of theexciting winding and a lower pole ring surrounding the lower part of theexciting winding the magnetizable annular member being arranged betweenthe two pole rings and the two single coils of the exciting winding,pole teeth on all three stator annular members, the rotor being providedwith the same number of teeth, said rotor being made in one piece tobridge all three stator annular members in an axial direction.

O'I'IO JANZEN.

